I'll start によって quoting Buffy herself, stating that she loved エンジェル もっと見る than she'd ever loved anyone in her life.

I'm also going to explain my preference によって criticising her other pairings. エンジェル gets criticised for making some decisions on her behalf, but I think the others are worse.

Riley

Firstly, I've a problem with her being paired with any normal human. エンジェル broke up with her so that she could have a normal human life - but she isn't a normal human. She's a slayer. Realistically, she's not going to survive long enough to grow old with someone. Same with being with someone who can give her...